BIOL 201 Midterm: midterm study2
20 Jul 2015
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Document Summary
Earth: life likely emerged from dna-based microbe that lived more the 3. 5 billion years ago. Increase in oxygen level had two important consequences. Some of the oxygen molecules in the outer layer of the atmosphere were converted to ozone (o3) molecules - when there is a sufficient quantity of ozone in the atmosphere, it absorbs ultraviolet rays (highly destructive to living organisms) By about 450 million years ago, the ozone layer apparently protected organisms sufficiently so they could survive in the surface layers of water and on the land, and life emerged on land for the first time. The increase in free oxygen opened the way to a much more efficient utilization of the energy-rich carbon-containing molecules formed by photosynthesis. Enabled organisms to break down those molecules by the oxygen-utilizing process known as respiration. All organisms, except archaea/bacteria, are composed of one or more eukaryotic cell. The origin of species: darwin was never able to explain how species might originate.
